The natural shape of human hair is generally classified into straight hair, wavy hair (wave hair), curled hair, and kinky hair (or coiled hair), depending on the degree of curl of the hair. Since the shape of hair and hairstyle constitutes one of the traits that can be easily recognized as physical features of human being, and also serve as an important factor that determines the first impression of a person, the shape of hair and hairstyle is a matter of great interest from a cosmetic viewpoint, irrespective of gender and age. In the case of kinky hair or curled hair with a high degree of curl, the person has trouble that the degree of freedom in hairstyle is limited so that desired styling cannot be achieved. On the other hand, even in the case of straight hair, the person also has trouble that the hair cannot be volumized, and bare skin is easily shown through.
As methods for changing the shape of hair and hairstyle, hairdressing using various hairstyling agents or hair dryers/hair irons, wave/straight permanent treatments, and the like are being extensively carried out. However, although these operations can effectively modify the shape of hair, the operations have no effect on the causative factor that determines the hair shape. These operations, which are the solutions to the above described troubles, are not fundamental solutions but are merely temporary, and in order to maintain the shape of hair and hairstyle, these operations must be repeated frequently. However, on the contrary, these operations cause increased damage to hair, and consequently impair the cosmetic value. For this reason, there is a demand for the development of a method for the intrinsic regulation of hair shape, by which the hair shape can be changed from the beginning of hair growth.
Searching for a causative factor that determines the hair shape and identifying a causative gene thereof are expected to provide useful information in the development of a method for the intrinsic regulation of hair shape. In regard to the factors or genes related to hair shape, there have been reports on the genetic diseases that bring changes to the shape of hair (Non-Patent Documents 1 to 3), acquired kinky hair caused by drugs (Non-Patent Document 4), curly hair model animals (Non-Patent Documents 5 and 6), an the like. However, the factors or genes disclosed in these documents are merely a special example which affect the hair shape, and are not adequate to be considered as causative factors that determine the natural shape of human hair.
Meanwhile, along with the rapid progress in the genome analysis technology in recent years, the correlation between diseases and genes is being gradually clarified. Particularly, not only for so-called genetic diseases that are defined by variation or abnormality of a single gene, but also for polygenic diseases characterized by low penetrance (the ratio of onset of a certain disease in an individual having a variation in a certain gene), such as highly frequent common diseases including lifestyle diseases such as diabetes and hypertension, search for causative genes using non-parametric linkage analysis techniques such as affected sib-pair linkage analysis is frequently carried out (see, for example, Non-Patent Document 7). Further, based on the hypothesis that the variation of a disease-associated gene for a common disease is a highly frequent genetic polymorphism (common variant), and that although the variation is present in healthy persons as well, the prevalence is significantly high in patients (Common Disease-Common Variant), search for causative genes by means of linkage disequilibrium analysis using a genetic polymorphism (for example, SNP (Single Nucleotide Polymorphism)) is also actively carried out throughout the world (see, for example, Non-Patent Document 8).
More recently, with the progress in the international HapMap Project, a database of general polymorphisms (SNP) of high frequencies such as one million loci or more in four human populations has been established, and research is being conducted on common diseases as well as on general traits in which the phenotype varies with the human race or population, for example, skin color, hair color, and eye color (see, for example, Non-Patent Documents 9 and 10).
Similarly, also in regard to the natural shape of human hair, it can be contemplated that the natural hair shape is a general trait in which the phenotype varies with the human race or population. In general, many Asian people have straight hair, while African people predominantly have kinky hair (or curled hair). Indo-European people have a high ratio of having a trait of wavy hair (wave hair), which is intermediate of the two. The mode of inheritance was first observed by Rostand, J., et al., and they reported that curly hair is an autosomal (semi) dominant trait over straight hair (Non-Patent Document 11). Furthermore, descriptions on the curly hair trait may also be found in the human Mendelian inheritance database of the NCBI (OMIM, http://www.ncbi.nlm.nih.gov/omim/). However, in regard to causative genes that determine the natural shape of human hair, systematic research on genome analysis has not been completed, and no such genes have been found yet.